Vapor Barrier

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anewbiewannabe

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So, I thought I'd toss this one out here after reading all the insulation and vapor barrier posts, since I haven't really seen it mentioned. So, the idea of a vapor barrier is to keep moisture/condensation away from something, given. In a vehicle habitation that something would be the interior of the metal walls, given. So, wouldn't it make some sense to install a vapor barrier next to those walls instead of on the interior before the final wall covering? Depending on insulation needs it could be easy or challenging. I just pose this because I know part of my year will be in humid environs and I am possibility thinking. Really though, it just popped into my head last night. :p

Opinions? :)
 

Free Range Chicken

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I think it's easy for humidity to get inside anywhere, unless it's very very very neatly sealed. (E.g. no lugs / bolt holes) And it's hard for it to get out of a poorly sealed cavity. I fear that'd cause a counterproductive situation where it'd get trapped and promote rust.
My approach would b more letting some air inside every cranny and crevice( through small gaps among the insulation panels) , so that a drive with the windows down will make air circulate and alleviate the issue.
Newbie here sharing my thoughts.
 

LeeRevell

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Since the basic idea is to keep moisture off the steel inner walls, would it not work to essentially paint the inner walls with a water-proof paint, perhaps a roofing sealer? Making sure to NOT plug any drain/weep holes at the bottom of curse.
 

SoulRaven

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Insulation on vehicles is much more complex than many would have you believe. The insulation has to breath, and the moisture needs to be wicked to the interior of the vehicle and away from the skin. If this is not accomplished correctly it will lead to moisture, mold, and rust problems in the future, which is of course hazardous to both your health and your vehicle's health.

A metal skinned vehicle will sweat, meaning that moisture will appear on the inside of the skin. NOTHING will stop this from happening. This moisture has to be dealt with for a successful insulation installation.

It CAN be done, but it is usually not worth it. Insulation works best when there is a constant heating or cooling source in the insulated space. This is simply not true in most vehicles. In most vehicles, Mother Nature is the most common constant source of heating or cooling, and therefore she will rule temperature wise in the end.

At best this insulation will only keep Mother Nature at bay for a few hours, at a cost in the thousands of dollars range. In the summer, simple ventilation will accomplish the same thing, and in the winter by morning it will be just as cold if not colder on the inside than it is outside, because that same insulation is fighting to keep the now warmer outside air out. It won't succeed, but it will keep you cold and miserable in the meantime.

No matter how much insulation you have, you still need good heating and/or cooling sources. The insulation does not eliminate that need. Too many people credit their insulation for staying comfortable when the real credit goes to the moderate climates they're in. When they're heavily insulated rig radiates heat all night in the summer, they think it's because they need more insulation, when in fact it's the insulation that's radiating that trapped and unwanted heat.

One of the beauties of window vans is that the manufacturer has already done the work for you. You start out with finished floors, walls, and ceilings, that have been designed to prevent moisture build up from the start. In the winter, those windows can act like solar heaters, and in the summer they can provide you with ventilation. You still need your heating/cooling devices, but you will need to use them a lot less.

When I switched from a heavily insulated cargo van to a window van, my winter heating costs got cut by over 30% thanks to the free heat coming in through the windows. In the summer I can open the windows and bring the temps down to comfortable very quickly in the evening, while the cargo van remained a sweat box for hours, even with all the doors open.

We can treat Mother Nature as either a friend or a foe. I learned a lot about this with my off grid cabin, and the exact same principles hold true for my camper vans. My whole Southerly half of my cabin is mostly windows. In the summer they are shaded by trees, and in the winter when the leaves fall off, they get full sunshine. On a sunny but cold winter day, the sun provides all the heat needed until sunset. In the summer, at 120° in the shade, through modified convective cooling, the indoor temps remain in the 70's. Mother Nature CAN be your friend if you plan things correctly.
 

anewbiewannabe

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Offgrid, thanks for so much detail. So an insulated metal vehicle would suffer problems just like a sticks and bricks, though different problems, if the interior air is not kept conditioned to a relatively small range of temperatures and/or if the moisture isn't wicked into the interior if I'm understanding correctly, which makes sense. I actually wondered about the walls sweating when I asked since our uninsulated van years ago would have dampness on the walls in really cold or really humid conditions, tents too---one of the reasons I asked.

I have some understanding of how to set up convective cooling in a passive solar sticks and bricks situation. It sounds like, because there is a greater likelihood for me having to stay in an area with higher temperatures and humidity part of the year, that figuring out the best ways to manage convection/conditioning for cooling of the van would be higher on my list than insulation maybe? More challenging than being able to put in a solar chimney, convective roof, or vent type situation though.

Thanks. :)
 

SoulRaven

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anewbiewannabe,

I just use a home made 12v A/C in my van, works like a charm, and unless it gets into the mid to upper 90's, the water only is sufficient.  Above that, and I add ice, which will last about 6 days, but I only need it once or twice a year normally.

12v_AC_3.jpg
 

907KHAM687

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Off Grid 24/7 said:
A metal skinned vehicle will sweat, meaning that moisture will appear on the inside of the skin.  NOTHING will stop this from happening.  This moisture has to be dealt with for a successful insulation installation.

Not just metal, any non permeable skin.
And the harder you try to prevent the condensation the worse you are going to make the problem. With a very good vapor barrier on the inside of the insulation, there wont be as much condensation on the skin on any given night, but the water that does condensate will be trapped. Forever.

Its very easy to reach the point of diminishing returns on insulation, I wouldn't go past two layers bubble wrap on a van. After that decent air exchange is going to steal more heat than can radiate out the walls. Which you need decent air exchange, it hurts to pump out hot air and let cold air in, but you have to get all the moisture out.

Hank
 

akrvbob

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I disagree with just about all the conclusions you all are reaching here.
Bob
 

SoulRaven

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907KHAM687 said:
Not just metal, any non permeable skin.  
And the harder you try to prevent the condensation the worse you are going to make the problem.  With a very good vapor barrier on the inside of the insulation, there wont be as much condensation on the skin on any given night, but the water that does condensate will be trapped.  Forever.  

Its very easy to reach the point of diminishing returns on insulation, I wouldn't go past two layers bubble wrap on a van.  After that decent air exchange is going to steal more heat than can radiate out the walls.  Which you need decent air exchange, it hurts to pump out hot air and let cold air in, but you have to get all the moisture out.  

Hank

The trick is just to have enough heat to compensate for the ventilation and to keep you warm at the same time.
 

Wabbit

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akrvbob said:
I disagree with just about all the conclusions you all are reaching here.
Bob

Bob, if you have a minute could you talk about your experience with heating/cooling issues and condensation? Reading Offgrids explanations seem to make sense to me, but I have no experience with this. And I know from other experiences that just because it sounds right, doesn't mean there aren't fatal flaws in the explanation. If that makes any sense.
 

anewbiewannabe

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Cry said:
Bob, if you have a minute could you talk about your experience with heating/cooling issues and condensation? Reading Offgrids explanations seem to make sense to me, but I have no experience with this. And I know from other experiences that just because it sounds right, doesn't mean there aren't fatal flaws in the explanation. If that makes any sense.

Thanks. I was going to ask the same because I've read Bob's stuff on insulation and it makes sense to me too. The only thing I've reached a conclusion on is that setting up good ventilation is important either way. :-/
 

vanman2300

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This all makes me wonder how the RV manufacturers handle this issue....,..
 

Almost There

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vanman2300 said:
This all makes me wonder how the RV manufacturers handle this issue....,..

They generally don't - most of the RVs made today have fiberglass panels on the outside which don't rust out, which is our concern with van walls.

That and the RV's are mostly manufactured with a life expectancy of just shortly more than the warranty, much like cars are made today! They certainly aren't made with a 20 or 30 year full-time living use in mind!
 

One Awesome Inch

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Another perspective...

 I am currently putting up 2 inches of polysterene on the walls and ceiling of my van. Then I am putting up a vapor barrier of heavy plastic sheeting over all of it. Hoping to not have any condensation issues as I live in a very humid climate where its often above 85% humidity.

The process is taking hours and hours.... and hours!

20150314_160532_zpsoim8zebt.jpg
 

907KHAM687

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I would guess that the disagreement would stem from the temperature different people find comfortable. My dad has the thermostat in is house at 76 all the time. He has the thermostat in his office at 76 all the time. It is worth it to him to pay for 24/7 heat at the office where he only spends 4 hours a day. He wants to walk in and be warm. I think he is crazy. I live in a old rv, with a Mr buddy heater. It's 40 degrees outside now, and maybe a couple degrees warmer inside as the last bit of heat from the sun flows out the open window, and I am comfortable. My dad thinks I am crazy. And I will admit, it gets a little rough at -10 but I can deal with it.

So the benefit of insulation is fairly minor for me. To my dad it would be a necessity. The risk of messing up an install would be the same for both of us, and however minor the risk might be, the piece of mind I would gain from not having to worry about water damage far outweighs any discomfort from the cold. My dad would accept that risk, being warm is a much higher priority for him.

And he has never ripped the interior out of the most beautiful 79 Chevy conversion van to discover the osb is totally saturated. I can honestly say that van was the nicest thing I ever owned. Its black paint was a black a a piano and twice as shiny. The seats were amazing, the futon in the back was a bit lumpy, but man that thing was perfect. And I ruined it.

Hank
 

One Awesome Inch

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I'm with your Dad. I want heat. Thus the reason for the overkill insulation (that and noise reduction). My plan is to run the Wave 3 @ 1600BTUs all the time I'm in the van.
 

Seraphim

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A house is not sealed against against outside air. The purpose of a vapor barrier is to prevent outside air from moving into the house, bringing in moisture. A van, I suspect, is different. While still not completely sealed, the welded body is much more airtight than a house, and it's smaller. The condensation problem is due to existing moisture inside the unit, some of it coming from a person exhaling. Some airflow is needed for the moisture to escape, such as a cracked roof vent, else the moisture will build up inside. I personally don't see the need for a vapor barrier in a vehicle: the vehicle body fulfils that function.
 

907KHAM687

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Seraphim said:
A house is not sealed against against outside air. The purpose of a vapor barrier is to prevent outside air from moving into the house, bringing in moisture. A van, I suspect, is different.  While still not completely sealed, the welded body is much more airtight than a house, and it's smaller. The condensation problem is due to existing moisture inside the unit, some of it coming from a person exhaling. Some airflow is needed for the moisture to escape, such as a cracked roof vent, else the moisture will build up inside. I personally don't see the need for a vapor barrier in a vehicle: the vehicle body fulfils that function.


No. The purpose of a vapor barrier in a building is to prevent the moisture rich air from inside the living area reaching the structure of the building. A nonpermeable exterior(vehicle body) performs the exact opposite, it traps moisture in the structure of the building.
 

vanman2300

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Exhaling is one of the top ways we lose water but a good vent fan will take care of most of it and any other forms of moisture as well. However, it seems to me the biggest problem is the skin of the vehicle temperature gradients that cause moisture within a closed space that will eventually form rot and mold.

Has anyone tried to leave an opening on the walls along the floor and ceiling for air to circulate through and remove the normally hidden moisture? Another good question, I think, is has anyone ever opened up the wall of their van after a few years and what did they find for damage due to moisture? I'm wondering if moisture should be a concern if the vehicle is bought used and the life expectancy is say only 5 years or so.
 
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